MaterialsgateNEWS
vom 25.11.2010

Verwandte MaterialsgateCARDS

Trained bacteria convert bio-wastes into plastic

Joint press release from NWO and TU Delft Researcher Jean-Paul Meijnen has 'trained' bacteria to convert all the main sugars in vegetable, fruit and garden waste efficiently into high-quality environmentally friendly products such as bioplastics.

He will be defending his doctoral thesis on this topic, which was carried out in the context of the NWO B-Basic programme, at TU Delft on Monday 22 November 2010.

There is considerable interest in bioplastics nowadays. The technical problems associated with turning potato peel into sunglasses, or cane sugar into car bumpers, have already been solved. The current methods, however, are not very efficient: only a small percentage of the sugars can be converted into valuable products. By adapting the eating pattern of bacteria and subsequently training them, Meijnen has succeeded in converting sugars in processable materials, so that no bio-waste is wasted.

Basis for bioplastics

The favoured raw materials for such processes are biological wastes left over from food production. Lignocellulose, the complex combination of lignin and cellulose present in the stalks and leaves of plants that gives them their rigidity, is such a material. Hydrolysis of lignocellulose breaks down the long sugar chains that form the backbone of this material, releasing the individual sugar molecules. These sugar molecules can be further processed by bacteria and other micro-organisms to form chemicals that can be used as the basis for bioplastics. The fruit of the plant, such as maize, can be consumed as food, while the unused waste such as lignocellulose forms the raw material for bioplastics.

Cutting the price of the process

"Unfortunately, the production of plastics from bio-wastes is still quite an expensive process, because the waste material is not fully utilized," explains Jean-Paul Meijnen. (It should be noted here that we are talking about agricultural bio-wastes in this context, not the garden waste recycled by households.) The pre-treatment of these bio-wastes leads to the production of various types of sugars such as glucose, xylose and arabinose. These three together make up about eighty per cent of the sugars in bio-waste.

The problem is that the bacteria Meijnen was working with, Pseudomonas putida S12, can only digest glucose but not xylose or arabinose. As a result, a quarter of the eighty per cent remains unused. "A logical way of reducing the cost price of bioplastics is thus to 'teach' the bacteria to digest xylose and arabinose too."

Enzymes

The xylose has to be 'prepared' before Pseudomonas putida S12 can digest it. This is done with the aid of certain enzymes. The bacteria are genetically modified by inserting specific DNA fragments in the cell; this enables them to produce enzymes that assist in the conversion of xylose into a molecule that the bacteria can deal with.

Meijnen achieved this by introducing two genes from another bacterium (E. coli) which code for two enzymes that enable xylose to be converted in a two-stage process into a molecule that P. putida S12 can digest.
Evolution

This method did work, but not very efficiently: only twenty per cent of the xylose present was digested. The modified bacteria were therefore 'trained' to digest more xylose. Meijnen did this by subjecting the bacteria to an evolutionary process, successively selecting the bacteria that showed the best performance.

"After three months of this improvement process, the bacteria could quickly digest all the xylose present in the medium. And surprisingly enough, these trained bacteria could also digest arabinose, and were thus capable of dealing with the three principal sugars in bio-wastes." Meijnen also incorporated other genes, from the bacterium Caulobacter crescentus. This procedure also proved effective and efficient from the start.

Blend

Finally, in a separate project Meijnen succeeded in modifying a strain of Pseudomonas putida S12 that had previously been modified to produce para-hydroxybenzoate (pHB), a member of the class of chemicals known as parabens that are widely used as preservatives in the cosmetics and pharmaceutical industries.

Meijnen tested the ability of these bacteria to produce pHB, a biochemical substance, from xylose and from other sources such as glucose and glycerol. He summarized his results as follows: "This strategy also proved successful, allowing us to make biochemical substances such as pHB from glucose, glycerol and xylose. In fact, the use of mixtures of glucose and xylose, or glycerol and xylose, gives better pHB production than the use of unmixed starting materials. This means that giving the bacteria pretreated bio-wastes as starting material stimulates them to make even more pHB."

Sie wünschen Material- und Technologierecherchen zu diesem Thema?

Mehr zu diesem Thema

One-step process derives raw material for fuels and plastic from plants rather than crude oil

Some researchers hope to turn plants into a renewable, nonpolluting replacement for crude oil. To achieve this, scientists have to learn how to convert plant biomass into a building block for plastics and fuels cheaply and efficiently. In new research, chemists have successfully converted cellulose -- the most common plant carbohydrate -- directly into the building block called HMF in one step.
The result builds upon earlier work by researchers at the Department of Energy's Pacific Northwest National Laboratory. In that work, scientists produced HMF from simple sugars derived from cellulose. In this new work, researchers developed a way to bypass the sugar-forming step and go straight... mehr

MU researchers working toward making biodegradable plastics from plants a reality

More than 20 million tons of plastic are placed in U.S. landfills each year. Results from a new University of Missouri study suggest that some of the largely petroleum-based plastic may soon be replaced by a nonpolluting, renewable plastic made from plants. Reducing the carbon footprint and the dependence on foreign oil, this new 'green' alternative may also provide an additional cash crop for farmers.
"Making plastics from plants is not a new idea," said Brian Mooney, research assistant professor of biochemistry with the MU Interdisciplinary Plant Group. "Plastics made from plant starch and soy protein have been used as an alternative to petroleum-based plastics... mehr

In an effort to develop a new source of sustainable energy, researchers at Polytechnic University have bioengineered a fuel-latent plastic that can be converted into biodiesel.

The Defense Advanced Research Projects Agency (DARPA), the central research and development organization for the US Department of Defense, has awarded the researchers $2.34 million to advance this innovative technology and transfer it to industry. The commercialization of the technology will lead to a new source of green energy to households worldwide.
Professor Richard Gross, director of Polytechnic University’s National Science Foundation (NSF) Center for Biocatalysis and Bioprocessing of Macromolecules (CBBM) developed the new bioplastic using vegetable oils. He also partnered with DNA 2.0, a biotechnology company specializing in gene synthesis, to develop enzymes that can both synthesize... mehr

A plastic cup that can be reused without washing it, simply because contamination has no chance to stick to the surface? A self-cleaning surface like that of the leaf of a Lotus plant is ideal for many applications and consumer products. These ideal natural properties can be imitated quite well now. Structuring a plastic or other surface is possible by using an ultra fast femtosecond laser. PhD student Max Groenendijk of the Applied Laser Technology Group of the University of Twente presents remarkable results with this new technique.
The secret of the Lotus leaf can be found in numerous tiny pillars with a wax layer on top. Water drops are lifted by these pillars, get into a spherical shape... mehr